Cape Town - With little more than a week to go before the cars hit the track in Melbourne, Lewis Hamilton concedes that only "time will tell" whether Mercedes can up their pace.
Although the reigning World Champs topped the lap count in testing, they lost out to Ferrari on the timesheets.
Kimi Raikkonen was quickest of all with a 1:18.634 while Valtteri Bottas was the best-placed Mercedes driver in third, 0.676s down.
The testing times have prompted Mercedes to state that Ferrari are the team to beat while the Scuderia insists it the Brackley squad.
As for Hamilton, he's uncertain as to how much more there is to come from his W08.
"Do we have more potential? I mean time will tell," he said.
"We've been focusing on trying to understand this car and getting the most out of it.
"As I've said, there's never generally been the perfect day, but there's more potential in the car for it to grow but I will say the others look very, very fast."
The Brit added: "I didn't feel like I got everything out of it [the car], so I could go faster.
"We did everything we needed to do and learned a lot, which is always a positive as some days you don't learn a lot.
"You chase your tail sometimes. But we learned a lot. I feel confident we've got everything we need from this test."